Recently, Light Emitting Diodes (LEDs) are attracting attention as light sources of backlight units used in notebook computers, monitors, mobile phones, TVs and LCD displays, or as illumination devices. In particular, recently, white light emitting diode devices (hereinafter referred to as ‘white LED devices’) using LEDs, which are advantageous from the viewpoints of color rendering, the environment, performance improvement and power consumption, have attracted attention. However, when such white LED devices are used as light sources for illumination, no efficient measure for adjusting Correlated Color Temperature (CCT) has been proposed.
For example, in the case in which a white LED device, implemented using blue light and a YAG-based yellow phosphor, is used, high-quality emotional illumination can be realized if the same type of white light is emitted, but white light having a different CCT is emitted according to a human's preference or the state of use. That is, when it is assumed that 4000 K is suitable for the morning, 6000K is suitable for the noon and 3000K is suitable for the evening, it is necessary to automatically or manually adjust the CCT of a white LED device for illumination. If such a function of controlling CCT can be effectively realized, emotional illumination capable of creating a unique atmosphere, as well as providing a basic illumination function of lighting indoor space, can be realized. Furthermore, emotional illumination based on the control of CCT may be applied to psychological treatment, for example, for the stabilization of the psychological state of a human, in combination with the control of luminance.
However, the prior art illumination devices have a problem in that the adjustment of CCT cannot be efficiently realized because they perform only a simple function of controlling illumination based on the intensity of surrounding illumination.